CRANSTON'S MILL POND, Va. -- There are signs of success at last in the long, hard push to restore the Chesapeake Bay. Crab populations are rebounding. Restored oyster reefs are taking hold. And dead zones -- areas so devoid of dissolved oxygen that they cannot support aquatic life -- are shrinking slightly. But federal and state budget problems pose a threat to the cleanup. Budget cuts have forced a search by bay advocates for ways to draw private money into the massive environmental restoration. And that's why so much depends on a 50-acre impoundment hidden in woods here 45 miles east of Richmond.